The present invention relates generally to methods and apparatus for cleaning semiconductor wafers, and more particularly to an improved rinse tank.
Integrated circuits are manufactured from semiconductor substrates, or wafers, on which transistors, resistors, diodes and other electrical circuit elements are formed. The production of integrated circuits involves a multitude of processing procedures performed on semiconductor wafers. One such process whereby ions are implanted on semiconductor wafers is the reactive ion etch (RIE) process. It is quite important in semiconductor manufacturing that particulates formed upon a semiconductor within one manufacturing process be completely removed prior to a subsequent manufacturing process. Traditionally, the wafers are cleaned and rinsed prior to and subsequent to each procedure. Cleaning and rinsing is required in order to stop the chemical reaction that occurs during etching and to remove the etchant chemical or other contaminant matter from the wafer surface. The complete removal of particulate residue from semiconductor substrates will enhance the functionality and reliability of the completed integrated circuits.
Methods by which wafers may be rinsed with deionized water are common to the art. These methods include static water overflow baths, quick dump rinse (QDR) baths and processes whereby additional energy is introduced to the bath through ultrasonic or megasonic agitation. Another method involves bubbling air or gas from the bottom of the tank across the surface of the wafers and relying on convection currents to agitate the water molecules and facilitate water molecule interaction with the face of the wafer. A recent study has indicated that as little as 20% of the water within such tanks makes contact with the wafers.
Additionally, the traditional cleaning and rinsing methods do not adequately remove particulate matter from the tank itself. When particulate contaminates and etching chemicals have bonded with deionized water molecules during removal from the surface of a wafer or substrate, they tend to cling to the sides and corners of the associated rinse tank. This is particularly true of QDR tanks.
Furthermore, as the size of semiconductor wafers increases, water consumption in rinsing and cleaning steps has increased exponentially. Larger wafers require larger tanks which tend to waste additional deionized water. Traditional cleaning and rinsing methods are often inefficient, consume too much deionized water, and waste time.
Accordingly, a need has arisen in the art for an improved rinse tank for use in cleaning semiconductor wafers or substrates. The present invention provides a rinse tank that substantially eliminates or reduces problems associated with the prior rinse tanks.
In accordance with one aspect of the present invention, a positive flow, positive displacement (hereinafter xe2x80x9cPFPDxe2x80x9d) rinse tank is provided with an external shell having five generally closed sides and an open top. An internal shell may also be provided within a lower portion of the tank. The internal shell is preferably provided with a configuration to receive wafer boats through the open top of the rinse tank. The internal shell may be sized to support two wafer boats. Each wafer boat may be filled with semiconductor wafers or substrates. When filled with water, the external shell is preferably sized large enough to completely immerse the wafer boats and wafers in water.
More specifically, in accordance with teachings of the present invention, two deionized water inlets may be provided at the bottom of the external shell, preferably at opposite corners. The deionized water inlets allow the rinse tank to be filled with deionized water while maintaining approximately equal hydrostatic force throughout the tank. Three compressed air fittings may also be provided at the bottom of the external shell. The compressed air fittings may be attached to three-eighth inch polypropylene tubing. Compressed air may be introduced into the polypropylene tubing and forced into the bottom of the rinse tank in the area between the external shell and the internal shell. The compressed air may be provided at a pressure of approximately fifty-six pounds per square inch.
In another embodiment of the present invention the internal shell may be provided with a plurality of small deionized water jet ports. The jet ports allow a mixture of water and air to be transferred from a chamber between the internal shell and the external shell to the open bath. As deionized water and compressed air are added to the chamber, the fluid pressure is increased and the mixture of deionized water and air is forced through the jet ports across the face of the wafers.
In still another embodiment of the present invention, a method for cleaning and rinsing semiconductor wafers is provided, including the steps of immersing a wafer boat with semiconductor wafers into a tank filled with deionized water, such that the semiconductor wafers are fully immersed in deionized water and introducing compressed gas into a chamber occupying a bottom portion of the tank. The chamber is preferably perforated with a plurality of jet ports to direct deionized water fluid flow across the surface of the semiconductor wafers. The resulting pressurized water jets contact the surface of the wafers for a predetermined amount of time to remove any loose particles, chemicals or any other undesired contaminants from the surface of the wafers.
Technical advantages of the present invention include providing a more efficient rinse tank to clean and rinse wafers in such a manner as to force as much as ninety-eight percent of the deionized water in the associated rinse tank across the surface of each wafer being rinsed. The rinse tank is designed to add velocity and direction to deionized water jets and results in much greater water to wafer contact, increasing the overall efficiency of the rinse cycle.
Another technical advantage of the present invention includes providing a reduced size rinse tank which conforms to the shape of the associated wafer boat. By decreasing the volume of the rinse tank, less deionized water is required per rinse cycle. Furthermore, by increasing the efficiency and decreasing the overall size of the rinse tank, the cleaning and rinsing processes are accomplished in less time than conventional methods associated with rinsing and cleaning semiconductor wafers.
Other technical advantages will be readily apparent to one skilled in the art from the following figures, descriptions and claims.